Friday, March 19, 2010

Finally, a word from the other side

It is ironic that the prior book I reviewed is a vehemently pro-global-warming polemic, and this next is just as vehemently anti-global-warming, just as polemical. The new book is Heaven and Earth: Global Warming; the Missing Science by Dr. Ian Plimer.

The author knows he has a very tough row to hoe, so he goes the proverbial extra mile (or ten): Where most books of scientific popularization have 200 or fewer references, he has more than 2,000, which he has put in footnotes rather than endnotes. I am glad. I prefer footnotes; I am disinclined to keep paging to the back of the book, and tend to read endnotes, if at all, after the rest of the book. I don't mind glancing down now and again to see if a note has more material than just a bibliographic reference.

Long before the debate over global warning, when the term "greenhouse effect" was still in vogue, I read an article in which the author stated that even if CO2 were to rise to 1% the temperature would rise no more than 4°C or 7°F. That is a lot but it not great as some claims we are hearing.

A point which Dr. Plimer makes, which he supports with this chart, is that most of the greenhouse warming that CO2 can produce has been accomplished before the amount reaches 100 ppm.

We have here a classic situation of diminishing returns. It is one point in the book that I'll treat in some detail, then follow with a more general survey. The key to understanding it is to look at the way the spectrum of CO2 changes with its amount. The following chart shows the visible and infrared spectra of oxygen, CO2, and water. These spectra are all normalized to some specific depth of the pure gas, probably one meter (though the reference doesn't say).

See how the green line for CO2's spectrum has just a few bands, and only three that are "strong"? Let us suppose that this is for one meter of pure CO2. The atmosphere has just under 400 parts per million (ppm) at present, which is one part in 2,500. That means one meter of gas is distributed in 2.5 km of atmosphere. The effective thickness of the atmosphere is about 5 km, if you allow for the rapid thinning of air with altitude. So this line is probably quite close to the actual absorption spectrum of all the CO2 in the atmosphere between the ground and space.

Now, what happens as CO2 concentration changes? I prepared a simple spectral band absorption model to show this. First, a numerical example. Let us assume that the "standard amount" absorbs 75% of the radiation at a particular wavelength. What happens when there is three times that amount? The approach is to take the proportion that is transmitted (1-0.75 = 0.25), take it to the third power to get the new transmission (0.253 = 0.0156), and subtract from 1 to get the new absorption (0.984 or 98.4%).

I prepared the chart below for an absorption band with a gaussian shape at low concentration, shown by the lower, black line. If the amount of gas is ten times as much, shown by the red line, there is a section with nearly 100% absorption, and the whole line is wider. With each increase by a factor of ten, the absorption band widens by a smaller and smaller amount. Going from the red line to the dashed orange line, though the amount of absorbing gas increases by a factor of 10,000, the total absorption increases only by about a factor of three.I designed this example so that the red line approximates the absorption of CO2 near a wavelength of four microns, at 400 ppm for the full depth of the atmosphere. The solid lines above that one are for 4,000 ppm (0.4%) and 4%, at which point the amount of influence CO2 might have on the atmosphere is doubled. Four percent is also the level CO2 might conceivably achieve if we burn all known fossil fuels. This would also lower atmospheric oxygen by nearly 2%; how likely is that? Nonetheless, I show, with the two dashed lines, what the absorption would be if the atmosphere were 40% CO2, and if there were nothing but CO2 in an atmosphere with four times the density of today's atmosphere; a situation 1/10th as severe as that on Venus!

One might then ask, how can it be that Venus's temperature is 500°C? First of all, Venus receives twice the sunlight that Earth does. This means its equilibrium, airless temperature would be 65°C or 150°F. The airless temperature for Earth (experienced by the Moon) is 5.4°C or 42°F. Earth's actual equilibrium temperature is about 15°C or 59°F, mainly due to water vapor.

Take a look at what water vapor (the blue line) does in the 4-line chart above. It absorbs all wavelengths longer than 10 microns, and about half of radiation longer than 1 micron. If water were a much larger amount of the atmosphere, it would absorb so much of the outgoing radiation that a much higher temperature would be needed to move the thermal radiation to a short enough wavelength to escape to space.

CO2 has a very low absorption band longer than 6 microns, which in a very thick atmosphere absorbs everything. The "valleys" between the peaks shown also "fill up", absorbing everything from about 1.5 microns on. It requires a temperature of about 500°C to overcome this absorption, for an atmosphere such as that on Venus.

This, then is the physical explanation of the "greenhouse effect". Greenhouse gases such as water, CO2 or methane allow most incoming, shortwave radiation to reach the ground. Radiation in the absorption bands of these gases just heats the gases themselves, and the air they are part of. For the heated ground to radiate its heat back into space, it must emit enough radiation to get through the greenhouse gases. The warmer the ground is, the shorter is the effective wavelength of its thermal radiation. Longwave energy absorbed by the greenhouse gases heats up those gases, and about half of that is radiated back to the ground, so the more absorption there is, the warmer the ground has to get to achieve thermal balance. Of course, all this is complicated on a real planet because much of the heating goes into producing wind, but all energy turns into heat sooner or later.

The final point on this subject is this. At the concentrations CO2 has ranged within throughout history, its greatest effect has probably never been greater than about 3 times its present value. In the distant past, it reached concentrations as great as 1% (10,000 ppm). During one such time there was an ice age! It is never likely to come anywhere close to 1% again. Now for a summary of Dr. Plimer's message.He is called a "denier" by some, those he might call "warmists". He makes the point that a belief in global warming has become like a religion to some. No matter what people call themselves, even atheists have strongly held beliefs about something, which they hold with religious fervor. Everybody believes in something, particularly those who deny it the loudest.

The little chart above shows average global temperatures for the past 2,000 years. I deliberately went to a source different from the ones Dr. Plimer uses. If you click on it to see the larger version, you'll be able to read the reference. This prominently shows the Medieval Warming, which was warmer than 1998, the warmest year since the Industrial Revolution began in the 1800s. With this and similar data, Dr. Plimer asks the questions, "How did it get so warm in the years around 900 and 1000, when CO2 was so much lower than it is today?" and "Why were the Little Ice Age of 1400-1850 and the late Roman period before 800 so much colder?" Unless these questions can be answered, his point is that temperature is not controlled by CO2.Then he shows the comparison graph above, on page 89. The lower half is a similar, but smoothed, chart showing the Medieval Warming and the Little Ice Age as they have been understood by climate scientists for many years. The upper chart is the infamous "hockey stick" chart produced by Michael Mann and his colleagues. This chart has been totally discredited by several scientists, but is the one used by the IPCC to base its conclusions that we are all in grave danger. Is it any surprise that Dr. Plimer and others deny there is much to worry about? or that they question the motives of the leading authors of the IPCC Report?

The structure of the book echoes its short title. The Sun (Heaven) has by far the greatest influence on weather and climate. Its variation due to the sunspot cycle and longer cycles (which periodically eliminate sunspots for 50-100 years) has a significant, well-measured effect on climate. After an introductory chapter and one on history, the Sun and influences on solar influx to Earth fill one large chapter. Other heavenly influences include cosmic rays; when the sun is weaker, its reduced magnetic field lets more cosmic rays get through, and average cloudiness increases, further reducing the amount of sunlight that reaches the ground. Cooling ensues. Warming follows a strengthened sun, amplified by a reduced cloud cover. The Maunder Minimum, a 70-year period almost without sunspots, was the coldest part of the Little Ice Age.

In his History chapter, he makes the point again and again that warming periods have been periods of increased productivity and expansion of species, and that cooling periods are marked by desertification, loss of species or mass extinction, and (in the Holocene at least) crop losses leading to reduction in human numbers. He repeats these points throughout the book, particularly in the Sun chapter, where he asks, if global warming was good for the early Romans, and even better for the late Medieval Europeans, why do IPCC scientists claim it will be bad for us?

The fourth chapter, also a long one, is "Earth". While he hits a lot of points, a big one is volcanoes. Mass extinctions seem to have occurred in sychrony with extra-large "supervolcano" eruptions that took thousands of years to burn themselves out. Each such episode produced millions of cubic kilometers of lava, and thousands of cubic kilometers of "stuff" was put into the atmosphere. A characteristic of volcanic activity is that it produces lots and lots of CO2, yet because of Sulfur oxides and solid matter also blasted into the sky, cooling is the result. By the time the cooling is over, earth processes have usually absorbed all the extra CO2 as well. But there is another, continuous source of volcanic activity, which arises in the Water chapter.

Before Water he spends a chapter on Ice, primarily the Snowball Earth period in the late Precambrian period about 700 million years ago (and perhaps another one 2,000 million years ago). Both occurred when CO2 was many times denser than it is today.

In the Water chapter he addresses the question, "Will the seas become acid?" If you measure the acidity of soda, water with a few percent CO2, it is definitely a weak acid. Not as strong as vinegar, but acid nonetheless. However, if you put almost any common kind of crust-forming rock, such as granite or basalt, in the soda, and cap it for a few weeks or months, the acidity will reduce and eventually turn to alkali. Even though granite is called an "acidic" rock, that is only with reference to basalt, which is more strongly alkaline.

Guess what forms the sea floor? Basalt. What is going on deep under the sea? For one thing, CO2 in sea water quickly hydrolyzes to bicarbonate (HCO3- ion), which is less acidic. Then bicarbonate reacts with basalt to change silicates to carbonates, except that much of it is captured by snails, clams and other growing sea critters to make their carbonate shells also. All these processes result in a sea that is distinctly alkaline.

There is a greater source of CO2 under the sea, however. The Mid-Ocean Ridge is an 80,000-km system of "spreading center" volcanism that runs through every ocean basin. The average spreading rate is 5cm/y. That results in 4 cubic km of new lava produced every year (that is 30 million tons per day). These sea-floor basalts erupt at a temperature near 1000°C. It takes a lot of water to cool them down to the 0-5°C temperature of the deep ocean. Many cubic km of water are heated continuously by this outflow. Each cubic km of lava has a lot of CO2 in it, which dissolves in the deep water. This water has been measured to have the capacity to hold a lot more CO2 than what these Mid-Ocean Ridge produces. This amount is much greater than what we are producing with all our industry. The fresh basalt reacts with some of it to keep the oceans alkaline.

A short chapter on Air challenges the entire notion of the "greenhouse effect". The radiation-in-radiation-out definition I gave above is different from what the author espouses. I don't stand with him on that one. I understand the term is a metaphor that isn't supposed to exactly equate CO2 or any other gas to the glass in a greenhouse. We all know greenhouses are more for keeping freezing or drying wind off the plants, and often have to be either heated or cooled, but they do tend to gather heat by differential radiation absorption, and this is the part of the metaphor that is useful.

In his final chapter, "Et Moi", he recapitulates his main points, and closes by asking "What if I am wrong?" Only the "wildest" of the "warmers" will claim that during the present century warming will be greater than 3°C, yet the Medieval Warming was 3°C warmer than today, with very salutary effects on all. The sea didn't wipe out coastal settlements and crops boomed. He winds up with 18 "even if" points, the last being, "Even if mitigation were as cost effective as adaptation, the public sector, which emits twice as much carbon as the private sector, must cut its own emissions by half before it preaches to us."

He started that chapter by stating, "...the greatest threat...is from policy responses to perceived global warming and the demolishing of dissent." I agree with him on this. Is he wrong, folks? Prove it. Use real data, not Mann-style "hockey stick" fraud. But I have skimmed the internet and seen mostly ad hominem fallacies against him in response to the points in this book. Their authors are a shame to the profession of science.